Density of Na3AlF6–AlF3–LiF–MgF2–Al2O3–Sm2O3 molten salt melt for Al–Sm alloy

Abstract

Samarium (Sm) has been widely used in making aluminum (Al)–Sm magnet alloy materials. The research team for this study developed a molten salt electrolyte system which directly produces Al–Sm alloy to replace the energy intensive conventional distillation technology. In this study, molten melt density was measured and operation conditions were optimized to separate Al–Sm alloy product from the fluoride molten melt electrolysis media based on density differences. Archimedes' principle was applied to measure density for the basic molten fluoride system (BMFS: Na3AlF6–AlF3–LiF–MgF2) electrolysis media in the temperature range from 905 to 1055 °C. The impact of temperature (t) and the Al2O3 and Sm2O3 addition ratio (w(Al2O3), w(Sm2O3)) in the basic fluoride system on molten melt density was examined. The fluoride molten melt density relationship was determined to be: ρ = 3.11701 − 0.00802w(Al2O3) + 0.027825w(Sm2O3) − 0.00117t. The test results showed that molten density decreases with increase in temperature and Al2O3 addition ratio, and increases with the addition of Sm2O3, and/or Al2O3 + Sm2O3. The separation of Al–Sm (density 2.3 g/cm3) product melt from the BMFS melt is achieved by controlling the BMFS density to less than 2.0 g/cm3. It is concluded that the optimal operation conditions to control the BMFS molten salt density to less than 2.0 g/cm3 are: maintain addition of Al2O3 + Sm2O3 (w(Al2O3) + w(Sm2O3)) < 9% of Na3AlF6, Al2O3/Sm2O3 ratio (w(Al2O3):w(Sm2O3)) > 7:3, and temperature between 965 and 995 °C.